feat: enhance security with IP banning, ownership checks, and SSRF protection

Add comprehensive security improvements across the application:

- **IP-based login protection**: Implement IP ban system tracking login failures, auto-banning after threshold exceeded
- **Ownership verification**: Add userID parameter to Delete/Update operations for posts and comments to prevent unauthorized modifications
- **SSRF protection**: Add URL and resolved host validation for image URLs in chat and OpenAI client
- **SQL injection prevention**: Add EscapeLikeWildcard utility to escape special characters in LIKE queries
- **HTTP security**: Configure server timeouts and add security headers middleware
- **Rate limiting**: Refactor to support configurable duration and per-endpoint rate limits for auth routes
- **Error handling**: Standardize error responses using HandleError and proper error types

internal/service/schedule_sync_service.go

@@ -115,7 +115,10 @@ func (s *scheduleSyncService) convertCourses(data *pb.ScheduleResultData) []*mod
 	for _, c := range data.Courses {
 		for _, st := range c.Schedule {
 			dayOfWeek := 0
-			fmt.Sscanf(st.Day, "%d", &dayOfWeek)
+			if _, err := fmt.Sscanf(st.Day, "%d", &dayOfWeek); err != nil {
+				zap.L().Warn("invalid day format in schedule sync", zap.String("day", st.Day), zap.Error(err))
+				dayOfWeek = 0
+			}
 
 			startSection := 1
 			endSection := 1